Cell movements are essential to the existence of essentially all eucaryotic cells. These movements must involve the interaction of force generating and structural constituents of cells. The force for many cell movements is thought to be generated by actin and myosin, two proteins known to participate in muscle contraction. Structural components of cells that may participate in cell movements have recently been discovered in a number of cell types. These proteins form structured gels when mixed with actin in vitro. Actin-binding proteins from Dictyostelium discoideum having subunit molecular weights of 30,000 and 95,000 daltons will be examined in this proposal. First, the hypothesis that these components are required for the movement of living cells will be tested. Monoclonal antibodies that bind to and inhibit the activity of these structural proteins will be prepared and incorporated into living cells. Measurements of the movement of those cells will test the requirement for the specific proteins. Second, the structure and actin binding activities of the 30,000 and 95,000 dalton proteins will be examined in detail using viscometry, sedimentation, and ultrastructural techniques. Third, the presence of the 30,000 dalton protein in cellular extensions, pseudopodia and filopodia, will be assessed using both biochemical and immunochemical approaches. The results will both test and extend our knowledge of the molecular mechanisms of cell movements. Since the cytoskeletal and contractile proteins of D. discoideum are homologous to those in both invertebrate and vertebrate cell types, study of their interactions and intracellular functions may have general significance. The panoramic importance of cell movements is verified by their prominence in developmental biology, cellular immunology, and oncology. Knowledge of the molecular mechanisms of cell movements will direct future studies of these phenomena in normal and pathological states, and may eventually contribute to development of therapeutic and diagnostic procedures.